It is well known that torque transmitted through, for example, a driven shaft can be measured using Hall effect devices or foil strain gages bonded to the shaft in strategic locations and acting as the variable resistors of a Wheatstone bridge. When, as shown in FIG. 5, terminals A and B of the bridge are excited by a voltage source, variations in the resistance of the stain gage resistors (shown with through arrows) result in a voltage at the output terminals C and D. When there is no flex in the shaft due to transmitted torque, the bridge is said to be “balanced” and there is no output voltage across the C and D terminals.
The question then arises: how does one transfer the data from a Wheatstone bridge and/or other sensors mounted on a rotatable shaft, and/or the signals derived therefrom, to a processor and/or display unit in the stationary electronics needed to condition, record, analyze and/or display the data?
The conventional wisdom is to use slip rings. More sophisticated solutions to this problem involve wireless transmission systems; see, for example, U.S. Pat. No. 8,264,374 to Obatake et al. issued Sep. 11, 2012 disclosing an RF digital data transmission system in a torque applying device using a rotary shaft. A disadvantage of RF systems is the possible need to comply with regulatory standard such as those coming from the Federal Communication Commission (FCC). Inductive systems are also known but they are less compatible with high rate digital signal transfer.